SET OF INSULATING SHEETS ON A CASING TO IMPROVE BLADE TIP CLEARANCE

Abstract

The present invention relates to a turbine stator of a gas turbine engine comprising a turbine casing (9), a turbine shroud ring (13) and a shroud ring support (11) connecting the shroud ring (13) to the casing (9). The stator is one wherein the support (11) is provided with an element that forms a heat shield positioned on the turbine side.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to a nonlimiting embodiment based on the attached drawings in which:

FIG. 1 shows an axial half section of one example of part of a gas turbine engine in the region of the high-pressure turbine immediately downstream of the combustion chamber;

FIG. 2 shows the displacement D of, respectively, the rotor blade tips and the stator elements that form the operating clearance;

FIG. 3 shows in greater detail and in an enlarged view that part of the turbine casing that is provided with an element that forms a heat shield.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 3 shows an enlarged detail of the mounting of the shroud ring 13 in the casing 9, incorporating the solution of the invention. The ring support 11 according to the example consists of a metal partition wall, such as an annular partition wall, of substantially frustoconical shape with the same axis as the engine. The support here is formed as a single piece but could equally consist of several ring sectors joined together to form an annular entity. The support 11 comprises radial flanges 11a and 11b for attaching the elements 13 that form the high-pressure or HP turbine shroud ring. Attachment according to this example is of the tongue and groove type. For the upstream fixing, towards the combustion chamber, the back of the elements 13 is shaped to form an axially opening groove 13a which collaborates with an axial return 11b1 of the radial flange 11b. The downstream fixing of the elements 13 is provided also by a groove 13b the external branch of which bears against an axial return 11a1 of the flange 11a and is held in position by clamps 17.

The upstream nozzle guide vanes 5 are fixed by bolts to the radial flange 11b.

The support 11 is itself mounted on the turbine casing 93 via a radial transverse flange 11c. This flange is inserted in the flange assembly 95 which connects the various elements of the casing 9. The support 11 does not have any active clearance control nor does it have any ventilation means for achieving this.

According to the invention, a heat shield has been positioned on the internal face of the support 11, that is to say on the face facing into the engine gas stream. The heat shield advantageously consists of a first sheet positioned parallel to the support wall 11 between the two radial flanges 11a and 11b. This sheet is secured by welding, brazing, screw-fastening or any other fastening means, to the support. The sheet 21 is distant from the partition wall 11 so as to form a cavity 21a. This cavity is preferably dead, that is to say that the gases it contains do not circulate. It is, for example, a closed cavity. The cushion of gas thus forms a thermally insulating mass. However, if appropriate, this cavity may contain another thermally insulating material. A second sheet is positioned in the same way, upstream of the flange 11b, on the internal face of the partition wall 11 some distance therefrom. It is welded, brazed, screw-fastened or the like to the partition wall and forms a dead cavity 22a with the partition wall 11. The mass of gas contained in this dead cavity thus forms a thermally insulating layer.

The support 11 is made of metal as are the sheets 21 and 22. In stabilized speed operation, the clearance between the blade tip 33 and the ring 13 is fixed and of a determined value. This clearance is the result of equilibrium between deformations of mechanical and thermal origin to which the moving and stationary parts are subjected. In transient conditions this equilibrium is upset. Particularly in the case of critical reburst, as explained above, during the phase of rapid reduction in speed, the temperature of the gases in the driving stream drops. Because of the heat shield, the response to the drop in temperature of the support is slowed by comparison with that of the setup of the prior art. This means that during the sudden reacceleration or reburst that follows, the radial displacement of the rotor as a result of the increase in centrifugal forces does not interfere with the elements of the shroud ring. There is no contact between the blade tips and the elements of the shroud rings. No wearing either of the blade tip rub strips or of the abradable surfaces of the elements is observed.

The results of testing have demonstrated that the solution is effective and that the machine efficiency is improved as a consequence. Furthermore, attaching sheets is not particularly expensive. Overall, the solution is effective and economical.

Claims

1. A turbine stator of a gas turbine engine comprising a turbine casing, a turbine shroud ring and a shroud ring support connecting the shroud ring to the casing, wherein the support is provided with an element that forms a heat shield positioned on the turbine side, and comprises a radial flange on just one side, via which flange it is fixed to the turbine casing.

2. The stator as claimed in the preceding claim in which the element forming a heat shield comprises a sheet forming a space with respect to the support surface.

3. The stator as claimed in claim 2 in which the space forms a dead cavity not swept by gases.

4. The stator as claimed in claim 2 or 3 in which said space contains a thermally insulating material.

5. The stator as claimed in claim 1, 2, 3 or 4 in which the support comprises, on the opposite side to said radial flange, a means for securing the elements of the shroud ring.

6. The stator as claimed in claim 5 in which the support is in the form of a frustoconical partition wall.

7. The stator as claimed in claim 5 in which the means for securing the elements of the shroud ring comprise two radial flanges sandwiching the elements.

8. The stator as claimed in the preceding claim in which the element forming a heat shield comprises a first sheet fixed between two radial flanges.

9. The stator as claimed in the preceding claim, in which the element forming a heat shield comprises a second sheet positioned axially between the means for securing the elements of the shroud ring and the radial flange for fixing the support to the casing.

10. A turbine engine comprising a turbine stator as claimed in one of the preceding claims.